A really neat generic function is sequence(state: next:). The best part is that it produces a sequence lazily by running a closure. ie, each step is computed. 

The function parameters are the initial state, to be passed to the closure, and the closure itself, which receives and inout state on each run. We can update the state on each cycle, adjusting it’s value if needed. The closure will be executer until nil is returned.

This is specially neat to, for instance, traverse the hierarchy of views. </p>

let seq = sequence(state: greenView) { (next: inout UIView) -> UIView? in
    let parent = next.superview
    next = parent != nil ? parent! : next
    return parent // The top most `parent` will be nil, stopping the execution of the closure

Lazy is good, and you can take a look at a quick example of sequence(state: next:) in this gist